The generic term "scroll machine" encompasses a class of positive fluid displacement apparatus which use orbiting involute spiral wraps formed on facing parallel plates to compress, expand, or pump a fluid. Although many designs for scroll machines exist in the prior art, very few have been successfully reduced to practice as commercially viable products. Some to the problems which have arisen in these development attempts are unique to the scroll machine, e.g., providing effective seals between the involute wraps and the end plates. However, other problems common to rotating machinery must also be solved. For example, as in any mechanical device having moving parts subject to friction and loading, it is necessary to provide proper lubrication to avoid excessive wear. In a scroll machine, an adequate lubricant supply is particularly important for the bearings asssociated with the rotating drive shaft and with the elements for converting the rotational motion of the shaft into the orbital motion of the scroll plates.
The lubrication system used in scroll machines and other rotating machinery having vertical drive shafts generally follow a similar pattern. Typically in such machines, oil flows from a reservoir located in the lower part of the machine housing through oil passages drilled or formed in the drive shaft, for distribution to the various components requiring lubrication. An example of such a design is disclosed in U.S. Pat. No. 4,065,279. As shown therein, a centrifugal oil pump forces oil from a reservoir up through two eccentrically placed oil passages bored in a vertical drive shaft. One of these passages supplies oil to a series of grooves associated with a swing link journal bearing, thereby lubricating it and an adjacent thrust bearing. Oil flowing in the second internal passage of the drive shaft is distributed through a right-angle passage for lubrication of the top journal bearing of the drive shaft. This design illustrates one solution to a problem shared by most designs for scroll machines--providing adequate lubrication to the thrust, swing link, and drivel shaft bearings--difficult due to the spatial separation of these bearings and the relatively dissimilar motion with which they are associated.
The lubrication requirements of the various types of bearings used in a scroll machine are substantially different. For example, roller bearings require very little lubrication, and in fact, experience frictional losses if supplied excessive oil. By comparison, a thrust bearing comprising a sliding surface requires substantially more oil flow. A lubrication system for a machine in which various types of bearings are used should thus allocate oil flow between the bearings according to their lubrication requirements.
In a scroll machine, part of the oil flowing through the delivery system to the orbiting scroll thrust bearing may be diverted to flow downward through the main drive shaft bearing. However, if conical or tapered drive shaft main bearings are used, oil will not flow through the bearing unless it is introduced at the end of the bearing where the rollers are radially closer to the drive shaft. Centrifugal force prevents oil flow through the conical bearing in the opposite direction. Thus, if cone bearings must be oriented to provide axial support of the drive shaft so that lubrication by gravity flow is not possible, another means must be found to introduce the lubricant into the bearing at the proper end.
One method of lubricating the main bearings as shown in the '279 patent, is to drill radial oil passages into the drive shaft intersecting the bore through which oil is delivered to bearings at the top of the shaft. There are several drawbacks to this approach, the most significant being that it diverts part of the oil flow away from the bearings adjacent the upper end of the shaft, e.g., the scroll plate thrust bearing. Also, the small diameter radial oil passage which intersects the bore may become clogged with contaminants, causing eventual damage due to lack of lubricant supply to the main drive shaft bearings.
In view of the foregoing, it is therefore an object of this invention to provide a lubrication system for lubricating the main drive shaft bearing of a scroll machine without diverting oil flow away from the other critical bearings in the machine.
It is a further object of this invention to provide a main drive shaft lubrication system that is both efficient and unlikely to fail due to plugging with contaminants.
A still further object of this invention is to supply lubricant to the proper end of a conical main bearing so that oil flow through the bearing is encouraged.
Yet a still further object is to recirculate oil through the main bearing prior to the return of the oil to a reservoir.